1. Field of the Invention
The present invention relates to flexible pouch packaging, and more particularly to apparatus for testing heat penetration into a flexible pouch package.
2. Description of the Prior Art
Sterilization of food to prevent bacterial growth and provide long shelf-life is a well-known practice in the canning industry. The sterilization takes place by thermally processing the packaged food at elevated temperatures for a predetermined time.
When packaging a particular food product for the first time, or when using a new package, such as a different size can, tests must be run to establish process specifications that will insure that all of the food in the package is sterilized. Recognized testing techniques require that the bacteria count be established after the container is exposed to different temperatures for different times. Accurate correlation of bacteria count with the time-temperature conditions actually experienced by the food requires measurement of the temperature inside the container.
The location within the container where the temperature is measured is also important because all of the food must be sterilized.
The measurement therefore should take place at that spot in the package that is the slowest to heat; for regularly shaped packages, the geometric center. If there is uncertainty over whether the measurement was taken there, there will be uncertainty over whether the processing actually sterilized all of the food. In that case, process specifications, to be safe, will have to call for thermal processing exceeding what the tests have indicated is necessary. Excessive thermal processing affects the product taste and is avoided whenever possible.
The same criteria for thermal processing and sterilization apply to flexible pouches as apply to the more familiar can or jar, except excessive thermal processing is especially to be avoided with flexible pouch packages. One of the benefits of a flexible pouch over more traditional packages is that its thin shape allows less cooking of the pouch to sterilize all of its contents than a can or a jar requires. That is so because the contents near the package walls do not get overcooked nearly to the degree that occurs in cans and jars just to cook adequately the food at the package center. However, that benefit cannot be fully realized unless a thermocouple can be held at a specific location inside the pouch, generally its geometric center. Without that capability, excessive thermal processing will have to be specified to be sure that all of the food in the pouch is adequately sterilized.
With a rigid container such as a can, the problems of holding a thermocouple at a desired location is not particularly severe. The can walls can not be moved to displace the product within the can. Because the can walls are rigid, a probe with a thermocouple at the end can be secured to the can walls to hold the thermocouple in place.
Wire holders have been used to position an indicator card, made of a time temperature-sensitive material, within a can during processing, as shown in U.S. Pat. No. 3,754,465 to Romito, et al. But that patent does not teach how to hold a thermocouple inside a flexible pouch package, but instead relies on the rigidity of the container to position a large, flat indicator card.
Maurice R. Berry, Jr., Ph.D., in "The Sterilization of Food and Pouches--Critical Parameters for Still Processing", a presentation for the symposium "Using the Retort Pouch--Worldwide", sponsored by the Food Science Institute at Purdue University on Mar. 14-15, 1979, at Indianapolis, Ind., discloses two devices used in an attempt to hold a thermocouple at the center of a flexible pouch. One of the devices was a coiled wire, with the helix diameter equal to the pouch thickness, secured to the pouch walls. The second device was an accordion-pleated web of material sealed to and spanning the pouch walls. The thermocouple was supported through a hole in the center of the web. Dr. Berry used the second device to take temperature measurements. However, both of those devices are somewhat cumbersome solutions to the problem because securing the device to the pouch walls requires manipulation of the device in the limited space inside the pouch.